1. Field of the Invention
The present invention relates to a damage detection system which detects damage such as defects and aged deterioration caused to a structural composite material applied to aircraft structures, space equipment such as satellites and space stations, high-rise buildings, public infrastructures, high-speed vehicles, and the like. The present invention also relates to a method of detecting damage to the structural composite material.
2. Description of the Related Art
In a field where both strength and weight reduction are required for a material, for example, airframes of aircrafts and the like, it is essential that a composite material such as Carbon Fiber Reinforced Plastics (CFRP) is widely applied in order to meet such requirements.
There has been disclosed, as an inspection apparatus to detect such as damage and defects caused to this kind of composite material, an inspection apparatus which includes film-shaped piezo elements and cables sandwiched between polyimide films (for example, see Patent Document 1: U.S. Pat. No. 6,370,964). This inspection apparatus is installed for inspection by embedding polyimide films having the piezo elements into the composite material of an unfinished structure, or by adhering the films to the surface of a structure with an adhesive. The inspection apparatus detects outputs from the piezo elements which are produced based on vibration applied to the structure, and detects such as damage and defects caused to the structural composite material based on the detected waveforms.
Additionally, detection processing apparatuses of a Fiber Bragg Grating (FBG) type, an Optical Time Domain Refrectable (OTDR) type, and a Fabry-Perot type, in which an optical fiber is used, can be given as examples of other earlier development. As shown in JP-Tokukai-2001-154069A (Patent Document 2), the diameter of an optical fiber is becoming finer and finer (for example, diameter of 52 μm) in recent years, and thus the strength of a structure is not reduced much even with the optical fiber embedded therein. Therefore, an optical fiber has an advantage that there is a high degree of freedom for installation thereof.
According to the earlier development described in Patent Document 1, to use the inspection apparatus, it is required that polyimide films be embedded in the structure or adhered to the structure with an adhesive, as described above. However, the polyimide films are flexible and easy to deform, and thus strength required for a structural material cannot be expected therefrom. Hence, lamination work thereof is complicated and thus increased.
According to the earlier development in which strain and the like of a structural composite material is detected using an optical fiber, influence of installation of the optical fiber, which causes reduction in the strength of a structure, can be suppressed to the minimum if the optical fiber with a fine diameter described in Patent Document 2 is used. However, in the earlier development, it is a local strain change in the vicinity of the optical fiber that what is recognized through inspection. Therefore, there has been a disadvantage that damage cannot be detected unless there is a local strain change.